1. Field of the Invention
The present invention relates to a droplet ejection head having a circulation flow channel, a droplet ejection apparatus including the droplet ejection head, and a method of collecting bubbles in the droplet ejection head.
2. Description of the Related Art
There are known inkjet type print heads (inkjet heads) in which ink is supplied to a plurality of pressure chambers from a common flow channel storing the ink, each pressure generating element is actuated to apply pressure to the ink inside a corresponding one of the pressure chambers, and the ink is ejected from a nozzle connected to the pressure chamber. In these print heads, a phenomenon known as fluid cross-talk is liable to occur whereby the pressure change affects the adjacent nozzles (and in particular, the meniscus therein) through the flow channels, and hence a structure which impedes the transmission of pressure to adjacent nozzles by arranging dampers inside the flow channels is used widely as a countermeasure to the cross-talk. However, in recent years, it has become difficult to introduce dampers due to the high density of the head.
In view of the aforementioned problems, Japanese Patent Application Publication No. 11-010911, for instance, discloses an inkjet recording apparatus in which air chambers are arranged in an ink circulation channel and a return channel, in order to alleviate pressure variation caused by a pump. However, such air damping devices generally need to ensure a prescribed height in order to make air enter into recording heads, and hence there has been a problem in that the ink volume becomes large. Moreover, since the air damping devices are disposed at locations distant from the nozzles, then although an effect in preventing pressure variation caused by the pump can be expected, the ability to damp the pressure variation produced by the ejection from the nozzles has been little.
Japanese Patent Application Publication No. 2005-145051 discloses an inkjet printer which suppresses pressure variation in the nozzles of a recording head by arranging compact damper devices. By arranging the damper devices, a large beneficial effect in suppressing fluid cross-talk can be expected; however, there is a problem in that the structure becomes complex and the manufacturing process is laborious.
Japanese Patent Application Publication No. 2000-117998 discloses an inkjet recording apparatus including an air damping device having an air storage unit in the vicinity of a recording head. The horizontal cross-sectional area of an ink storage unit is made smaller compared to the air storage unit so that increase in the ink capacity is prevented; however, since there is a large air storage unit, then it is difficult to align heads or compactify heads. Moreover, similarly to Japanese Patent Application Publication No. 11-010911, since there are no dampers in the vicinity of the nozzles, then it is thought that there is little beneficial effect in suppressing fluid cross-talk.
Japanese Patent Application Publication No. 07-125235 discloses an inkjet head in which a damper chamber is arranged in a portion of the common liquid chamber of an inkjet head, and pressure variation produced in the common liquid chamber is absorbed by this damper chamber. Moreover, a method of producing bubbles is also disclosed in which bubbles are generated by producing film boiling in the ink by means of a heater. However, there is no investigation into an inkjet head having a circulation flow channel.